The path to power

It’s easy to feel left in the dark when it comes to knowing what to look for in selecting a jobsite generator, says Pam Meyer, Subaru Robin Equipment Sales Manager.

“Surrounded by loads of choices, many feel powerless to make the right decision,” she says. “Don’t accept an across-the-map recommendation when selecting a generator. Each jobsite has a specific load size and that can affect the type of generator that would work best. The challenge comes in identifying those needs and matching it to a generator with similar capabilities. Overcoming that challenge will place you and your crew in a position of power at all times.”

Do the math
When looking for a generator, there are more numbers to crunch than just checking the budget and some price tags; and the physical size of a jobsite is not one of those numbers. A smaller job may require more power than a larger job.

“When considering a generator’s use, think through what tools you will need or want to power. First, list what the generator should power, such as circular saws and a welder. Find the silver tag attached to each tool to check the wattage, then write that number on a list and multiply it by the number of units to be used,” Meyer suggests. As an example, two hand drills that use 600 watts each would need 1,200 watts of power to run both.

Some tools take more energy to start than they do to run. This surge of wattage also should be taken into account when determining the total power needed. For example, hand drills and electric welders run on a constant wattage, while circular saws and air compressors need greater energy to start. A typical list may look like the table below.

To allow for error or future power requirements, consider adding 10 percent to the total calculated. In the example on page 30, the total would then indicate that a generator that can handle 8,800 watts – or 8.8 kilowatts – would be needed.

Some tools may have power listed in amps and volts, rather than watts, and horsepower might be used for motor-driven equipment. Some relatively simple calculations will convert these numbers into watts. If volts and amps are listed on the appliance, multiply the two to determine the wattage: amps x volts = watts. When horsepower is listed, use this wattage chart:

“Keep in mind that motors may need up to four times as much power to start as they do to run. Speak with an equipment dealer in order to get the exact specifications for a particular motor,” Meyer says.

Other important selection criteria
Once you’ve calculated your electrical load, it’s time to start shopping the features of generators in your power range.

Technological advances have made generators quieter and cleaner than ever, but there are still several degrees of “quiet” and “clean” – and the quieter the model, the more it will likely cost.

Inverter generators offer extremely quiet, clean power and are well suited to power sensitive electronics. The power runs through an inverter board, producing purely manufactured power. Inverter technology may be the right fit for a job if it’s in a severely noise-restricted area.

If you are looking to conventional generators, look at units that have quality components designed to reduce noise levels. Look for large mufflers and air cleaners built to suppress noise and automatic idle control, which will slow the engine when power isn’t being drawn.

When it comes to “clean” power, conventional generators use automated voltage, with a regulator controlling the voltage level and thus keeping the power more stable, or “clean.” Sensitive electronics run best on clean power since voltage fluctuations can cause computers to reboot or affect components that will later need to be recalibrated.

For construction sites, however, consider a capacitor-style generator. The power level is sufficient for power tools and air compressors, even though it would not be recommended for powering electronics.

The difference between generators’ “cleanness” can be found on sine wave charts. A sine wave is one standard cycle of electric current, or 60 hertz cycles per second. Sensitive electronics can handle a sine wave distortion of up to 10 percent, making conventional generators a good fit. Capacitor-style generators can have sine wave distortion of up to 40 percent, which is adequate for tools and other less-sensitive equipment. Inverter generators provide the lowest sine wave distortion of all styles with less than 2.5 percent, making them the cleanest of the three.

Meet jobsite demands
Generator quality can greatly affect its performance and dependability. A number of components indicate a well-built machine.

“First, a quality generator needs a quality engine – it won’t matter how well the rest of the generator has been constructed if the engine isn’t sound. Look for a company with a strong reputation for engine and generator reliability and a solid warranty. A fuel-efficient engine will cost less to run and prevent frequent refueling and downtime. A generator with auto-idle control conserves even more fuel since the engine will idle when power is not being drawn from the system,” says Meyer.

Check the thickness of the steel frame as well as the durability of the fuel tank. Look for well-built starting components – either an easy-to-pull recoil starter or an electric start. Count the outlets – will there be enough to power everything adequately?

An expansive control panel is a sign of a better quality machine. Look for an hour meter to help keep track of maintenance checks and services, while a voltage meter will eliminate guesswork. Using a generator with the largest fuel tank available for its size will lessen time spent refueling, while finding a generator with a fuel tank gauge will simplify checking fuel level. Additionally, a low-oil shutdown will guard against letting the lubrication level drop too low, which may result in engine damage.

Although it’s a minor component, a lifting eye is a nice feature because it allows the generator to be hoisted by a crane at the end of the day to prevent late-night theft.

OSHA and EPA compliance
While it may not be the first thing to come to mind when looking for a generator, it is important to ask if it is OSHA- and EPA-compliant. The Environmental Protection Agency has established three levels for emission control standards – Tier I, II and III – with deadlines for each tier of increased standards to be reached. OSHA sets regulations for ground fault circuit interrupters (GFCIs) which help protect operators from electrocution when used on a generator with a frame that can serve as a grounding electrode. The GFCI will compare the amount of current going to electrical equipment with the amount of current returning along the “grounded neutral.” If the difference between the two streams of current is greater than 5 milliamps, the GFCI will trip and stop the current.

While the GFCI will not protect against short circuits and overloads, conventional generators will pop a circuit breaker when it becomes overloaded, killing the outflow on the receptacle. On an inverter generator, a digital display will show “overload” and the engine will stop. The generator would need to be shut down and reset once the load was reduced.

Published in the September/October 2006 issue of Contractor Tools and Supplies magazine.

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